The invention relates to a double seal packer for subterranean wells which can be used to isolate two zones in an annular space of such wells.
The use of radially expandable packers, or annular seals, is known in the art. Such devices are frequently used, for example, to seal off a particular formation from the annular space of the well to facilitate hydrocarbon production through a production tubing of the well.
These packers operate through the application, by conventional means, of a compressive force to an elastomeric packer element which, upon longitudinal compression, expands radially to contact the walls of the casing of the well, and effect the desired seal of the annular space at that portion of the well. It has been found, however, that when operated under conditions of extreme temperature the elastomeric seal tends to extrude and reduce the effectiveness of the seal. Such extreme temperatures may be encountered, for example, during steam treatment of a well, or in deep wells which may have oil and sand temperatures in the range of 250-300.degree. F.
Several devices have been proposed attempting to deal with the problem of extrusion of the elastomeric material in order to obtain more effective seals.
For example, U.S. Pat. No. 4,730,835 discloses an anti-extrusion seal element using backup seal elements made of a knitted wire mesh and located at either end of an elastomeric material.
The recurrent heating and cooling accompanying steam treatment methods affect the ability of the elastomeric material and the knitted backup elements to expand and contract as desired, and therefore adversely affect the integrity of the seal achieved by the packer. Further, after a packer of this type is radially expanded in the well bore and subjected to extreme temperatures, the packer may not properly relax after compression is removed, and may therefore require a recovery procedure which increases the down time of the well during treatment.
U.S. Pat. No. 4,326,588 likewise discloses a radially expandable packer wherein an elastomeric material is prevented from extrusion by knitted elements similar to those in U.S. Pat. No. 4,730,835.
U.S. Pat. No. 4,531,581 discloses a piston actuated high temperature well packer wherein elastomeric elements are made of heat resistant material, such as asbestos, and a compression force is achieved through hydraulic means.
Large amounts of gravel or sand are frequently generated within the well during gravel and/or steam injection packing. Thus, another disadvantage in the known art is that the above-described devices are all complicated in nature and susceptible to malfunction when subjected to large volumes of gravel or sand in the well. This gravel also adversely affects the ability of the elastomeric elements of the prior art to maintain the desired seal.
It is thus the principal object of the present invention to provide a radially expandable packer for subterranean well installations which establishes a double seal which is resistant to the effects of fluctuating temperature.
It is a further object of the present invention to provide such a packer which is simple in structure and resistant to the adverse effects of gravel or sand which may be present in large amounts within the well.